add string representation to the Symmetry class

ippisite/ippidb/models.py

@@ -143,6 +143,9 @@ class Symmetry(models.Model):
     class Meta:
         verbose_name_plural = "symmetries"
 
+    def __str__(self):
+        return '{} ({})'.format(self.code, self.description)
+
 class Ppi(models.Model):
     ppi_id = models.IntegerField('PPI identifier')
     complex_id = models.ForeignKey(ProteinDomainComplex)